The present invention relates to a catalyzer arrangement in an exhaust system of a multi-cylinder internal combustion engine, particularly relates to an improvement of a catalyzer arrangement in an exhaust system of a multi-cylinder internal combustion engine for raising output of the internal combustion engine while lowering emission.
Hitherto, an exhaust system of a multi-cylinder internal combustion engine having a catalyzer arranged midway of an exhaust pipe has been known by Japanese Laid-Open Patent Publication Hei 6-10146. This exhaust system comprises an exhaust manifold, a catalyzer provided on a downstream side of the exhaust manifold and an exhaust pipe provided on the downstream side of the catalyzer. The catalyzer is so formed that exhaust gas discharged from the exhaust manifold flows in parallel with an output shaft of the engine, and the exhaust pipe is directed in a predetermined direction so as to discharge the exhaust gas into the atmosphere.
In the above-mentioned exhaust apparatus, an exhaust manifold having an exhaust pipe length (single pipe length) effective for the output and a catalyzer for purification of exhaust gas are provided in a limited space of an engine room to raise output of the engine while lowering emission.
However, according to the above exhaust apparatus, in case of an exhaust system in which a plurality of exhaust pipes (four exhaust pipes for example) connected to exhaust ports of an engine are collected into a collective exhaust pipe (exhaust system of 4-1 construction), it is difficult to ensure an exhaust pipe length sufficient for reducing exhaust gas interference accompanying high output of the engine within a space limited by breadth of the engine.
If it is intended to ensure a sufficient exhaust pipe length, it becomes difficult to ensure a space for arranging the catalyzer or to ensure a sufficient catalyzer capacity. In addition, since a distance between the exhaust port of the engine and the catalyzer becomes long, the catalyzer takes much time to reach the minimum active temperature and emission is increased.
The above circumstance is similar about an exhaust system in which a plurality of exhaust pipes (four exhaust pipes for example) connected with exhaust ports of an engine are collected into intermediate collective exhaust pipes every two pipes then the intermediate collective exhaust pipes are collected into a final collective exhaust pipe (exhaust system of 4-2 construction). Anyway, until now, it was difficult that high output and low emission are made compatible in an internal combustion engine.